_mask_filter_result function

hello, can anyone tell me what "_mask_filter_result" function is doing in edges.py (skimage/filer/edges.py), i am getting error when i am calling sobel edge detector in latest version of scikit-image . and why we are using it , i mean in sobel edge detection after applying the convolution , can't we directly return that new matrix. Thanks Umesh Kumar Sharma 4th year UG student CSE IIT kharagpur